def my_fun(s):
	result=[]								#定义空列表
	for i in s:								#遍历参数字符串
		if i not in result:					#如果当前字符不在结果中
			result.append(i)				#将当前字符添加到结果
	return result							#返回结果
print("hello world：",my_fun("hello world"))
print("welcome to china：",my_fun("welcome to china"))